This invention relates generally to hydrocarbon solvent solutions of alkylaluminoxane compounds and more specifically to a process for preparing stable, hydrocarbon solvent solutions of alkylaluminoxanes by reacting a mixture of trimethylaluminum and an alkylaluminum compound with water or a hydrated compound.
Hydrocarbylaluminoxanes complexed with transition metal compounds have been found to be very effective olefin polymerization catalysts (Manyik et al. U.S. Pat. No. 3,242,099). Methylaluminoxane is an especially effective catalyst component. However, it has poor solubility in aliphatic hydrocarbon solvents which are preferred catalyst solvents because they are less toxic than aromatic hydrocarbons. Manufacturers of polymers which may come in contact with foodstuffs are concerned about solvent residues in their products and therefore seek to avoid the use of aromatic solvents during polymer production. Even in aromatic solvents, methylaluminoxane is not completely soluble such that the solutions become cloudy upon standing. Japanese application 63-87717 discloses the addition to aluminoxanes of branched chain alkylaluminum compounds in order to improve the solubility of aluminoxane compounds which can be formed from mixed alkoxyaluminum units which contain methyloxyaluminium compounds in proportions of about 30 to 70 mole percent. Long U.S. Pat. No. 3,639,378 discloses an aluminum trihydrocarbon compound modified with water where the hydrocarbon groups can be alike or different. Edwards, et al U.S. Pat. No. 4,772,736 discloses a process of preparing aluminoxanes by adding water to a solution of a hydrocarbylaluminum compound such as isobutyldihexylaluminum or diisobutylhexylaluminum. Sakhorovskaya et al, Zhurnal Obshchei Khimie, Vol. 32, No. 10, pp 3433-3438, October 1984 discloses the hydrolysis of sesquihexylisobutylaluminum to give monoisobutyltrihexyldialuminoxane. Chang U.S. Pat. No. 4,937,217forms a mixed solution of trimethyl- and triethylaluminum in an aliphatic solvent with non-dehydrated silica gel to get a solid catalyst component of silica gel coated with aluminoxane. Kioka, et al. European published application 279,586 discloses forming finely divided aluminoxanes wherein one or more trialkylaluminums are directly reacted with water in a medium such as benzene, toluene, ethyl ether or tetrahydrofuran and then either adding an aluminoxane insoluble or sparingly soluble solvent, e.g., a linear or branched chain aliphatic hydrocarbon to the aluminoxane solution or spray drying. U.S. Pat. Nos. 4,189,402, 4,377,720 and 4,490,514 disclose aluminoxanes having mixed alkyl groups. Co-pending application Ser. No. 598,117, filed Oct. 16, 1990, provides improved hydrocarbon solvent solutions of alkylaluminoxane by adding a tri-n-alkylaluminum to preformed methylaluminoxane.
We have found a direct method for making clear, stable solutions of methylaluminoxane (MAO) compositions in hydrocarbon solvents and especially in aliphatic hydrocarbon solvents. The compositions have good activity as a polymerization catalyst component.